A surface light emitting element is exemplified as a novel light source. In order to improve a light extraction efficiency in a surface light emitting element, optimization of the structure of the light extraction efficiency has been considered.
One of the causes of the loss of light that has been generated in a surface light emitting element is plasmon loss that is caused by the adjacency of a light emitting layer and a metal electrode. In this plasmon loss, the loss can be decreased by distancing the light emitting layer from the metal electrode. It is also possible to decrease plasmon loss by adopting a structure having thick organic functional layers (for example, an electron transport layer and the like), or a structure in which a transparent electrode is interposed between a light emitting layer and a metal electrode.
When the cause of plasmon loss is decreased, the cause of decrease of an efficiency by a waveguide mode is increased. In order to solve the problem in a waveguide mode, light is extracted by providing a diffraction grating and a scattering layer.
JP 2004-14530 A (Patent Literature 1) discloses a structure of an organic EL element in which a light scattering layer having a high refractive index is provided to the side of a transparent electrode from which light is extracted. JP 2004-127942 A (Patent Literature 2) discloses a structure of an organic light-emitting diode device of a high light extraction type, in which transparent electrodes are provided to the top and bottom of a light emitting layer, and a light scattering layer is provided to between the side of the transparent electrode from which light is extracted, and a substrate.